Polyisocyanurate (PIR) and polyurethane (PU) foams are used extensively for insulation and other commercial applications. Often these materials are used in situations where fire retardant properties are needed or required by law. For example, some building codes require building walls and roofs containing these products to withstand fire penetration for up to one hour. However, these foams are not sufficiently fire resistant unless they are protected with a thermal barrier, such as gypsum.
Mesoporous structures are high-surface area porous oxides, such as silicon oxides, having an average pore size of not greater than about 100 nanometers as calculated using the nitrogen adsorption/desorption isotherm, as disclosed in Stucky et al., US Patent Publication 2009/0047329. Some mesoporous oxide structures can be prepared in the form of mesocellular foams. These mesoporous structures are relatively inexpensive to prepare, are easy to handle, durable, have high resistance to photo-induced corrosion and are heat resistant.
Mesoporous structures are generally prepared by exposing a source of a metal or metalloid oxide, such as silicon oxide, for instance tetraethylorthosilicate, to cross-linking conditions with a micro-emulsion or emulsion of surfactants, and optionally micelle swelling organic solvents, in water. The metal or metalloid oxide (such as silicon oxide), crosslinks on the surface of the micelles, which may include a micelle swelling agent, to form the basic mesoporous structure. The size of the pores is related to the size of the micelles formed. The size of the surfactant micelles can be adjusted by swelling with one or more micelle swelling organic solvents. The mesoporous structures are separated from the aqueous reaction medium and the default procedure used in the literature exposes them to temperatures at which any organic materials are removed by volatilization and/or burning them out. The structures of the mesoporous materials could be altered by heating them to temperatures at which they undergo calcination, for instance up to 500° C.
The mesoporous structures are comprised of cross-linked silicon oxide units, preferably silicon tetraoxide (SiO4) units. In essence chains of silicon oxide are prepared with crosslinks between the chains. In cross-linked structures a significant number of the silicon oxide units have three or four of the oxygen atoms further bonded to other silicon atoms. The cross-linked silicon oxide units are formed into structures comprised of walls forming pores which may exhibit any cross sectional shape useful in mesoporous structures, for example irregular, circular hexagonal, lamellar, and the like. These pore-forming structures may be interconnected by cross-linked silicon tetraoxide structures which are in the form of struts. The struts connecting the pore-forming structures create open areas between the walls of the pore-forming structures and the struts commonly referred to as windows. Structures containing a high percentage of these interconnected pore forming structures may be referred to as foams because they have relatively high pore volume and consequently low density. The formed structures contain a plurality of the connected pore forming structures connected by a plurality of struts and demonstrate tortuous open paths through the structure. Mesoporous structures are generally accepted to have pores having a size of about 2 nanometers or greater and a size of about 100 nanometers or less, and preferably about 50 nanometers or less as defined by IUPAC.
It would be advantageous to develop heat resistant materials, such as polyisocyanurate and/or polyurethane foams, that did not require the use of a thermal barrier.